A hook-and-loop type fastener is a well know mechanical fastener and wildly used in a variety of fields that need to fasten two separate parts together, such as garment, hats/caps, shoes, personal care product (such as diapers) etc., because of its easy engaging/disengaging characteristic. Recently, traditional hook straps are replaced with injection molded hook straps in the hook-and-loop fastener market because the injection molded hook straps are not only lighter and thinner than traditional hook straps, but also posses advantages over traditional hook straps, such as providing larger lateral pulling strength/peel-off strength, causing less loosen threads during processing, providing higher finished product quality. Additionally, while processed with post-processing process, such as printing, dying, high frequency processing, the injection molded hook straps can provide more add-values, such as providing an artistic appearance and showing the brand name etc.
Although existing injection molded type hook straps are wildly adapted in a variety of applications because of possessing advantages mentioned above, they are still unable to meet various needs in different fields because the structural deficiencies of the hook itself causes problems and limitations, such as stress concentration, destruction of the hooks and the loops, insufficient lateral engagement strength, etc.
Specifically, FIG. 1 schematically shows an illustration of an existing injection molded hook 1 including a hook body 2 which is relatively inflexible and substantially perpendicular to a substrate 3 of a hook strap. Curved portions of the entire hook 1 only exist at the hook neck 4 and the hook end 5. When the hook end 5 disengages with the loop 6, the disengaging force will concentrate at the hook neck 4 because the hook body 2 stiffer than the hook neck 4, and this in turn will cause the hook neck 4 and hook end 5 to deform to a degree that exceeds the yield strength of the plastic material of the hook and thus produces plastic deformation of the hook end 5. Therefore, the hook neck 4 and hook end 5 will be gradually straightened such that the hook 1 is unable to effectively engage with the loop and the engagement strength is thus weakened, and then the hook strap will lose its fastening function in the end.
Additionally, if the loop 6′ does not engage with the hook 1 at the hook neck 4 or the hook end 5 but at the hook body 2, then when the loop 6′ disengages with the hook 1, the interaction force between the hook loop 6′ and the hook 1 will occur at the relatively rigid and inflexible hook body 2. Because the interaction force acting on the hook body 2 is unable to be properly relieved by an elastic deformation of the hook body 2, the disengaging force turns into a lateral pulling force and causes the hook 1 and the loop 6′ to pull each other. This lateral pulling force will break the hook 1 and/or the loop 6′ and thus dramatically shorten the effective lifetime of the hook strap.
Moreover, the shape, the arrangement and the density of the injection molded hooks of the hook strap will affect the loop strap that cooperate with it. During the engagement of the hook strap and the corresponding loop strap, the number of hooks of the hook strap that engage with the loops of the loop strap is the main feature that affect the fastening effect of the hook strap. Therefore, providing a hook strap with consistent and strong engagement strength is one of the goals that the fastener strap industry have been continuously try to reach.
In addition, during the engagement of the hooks and the loops, a change in engaging direction and engaging angle between the hooks and loops will cause single-direction injection molded hooks failing to engage with the loops. And, this problem relates the curvature of the hook arm and the distance between the hook end and the hook body. In other words, the distance between the hook end and the hook body and the length/curvature of the hook arm will affect the engaging/disengaging efficiency between the hooks/loops. Therefore, solving the fail-to-engage problem of the single-direction injection molded hooks caused by different engaging directions and angles during engagement by properly altering the fundamental structure of existing injection molded hooks is also one of the issues that the fastener strap industry is looking forward to accomplish.